As the oral hygiene device, for example, in an electric toothbrush there are known a first type electric toothbrush in which a vibration is applied to a replacement brush by rotating an eccentric weight by an electric motor, a second type one in which a rotary motion of an electric motor is converted to a liner motion through a cam or the like, thereby reciprocating the replacement brush, and a third type one in which, as disclosed in Japanese Patent Unsearched Publication No. 7-505069, DC current supplied from a battery or the like is converted to AC current by an invertor and supplied to a coil, thereby vibrating the replacement brush by alternating field of the coil.
Although the first type electric toothbrush has a simple structure and can be produced at low cost, since the vibration is transmitted to the replacement brush through a casing for accommodating the electric motor and battery, a part of the vibration is transmitted to fingers via the casing, so that a sufficient amplitude at hair tips of the replacement brush cannot be obtained and, therefore, there is a problem that eventually it performs only a supplemental action for manual brushing. Further, since vibration frequency of the replacement brush becomes the same as a rotation number of the electric motor, the vibration frequency of the replacement brush is difficult to be changed.
Although the second type electric toothbrush can provide a vibration which is more similar to actual brushing because the rotary motion of the electric motor is mechanically converted to the linear reciprocating motion using a cam or the like, the structure is complicated and production cost becomes high and, in addition, it is considered that if a large load is applied to the replacement brush, the electric motor is overloaded, so that it may be damaged. Further, it involves a problem that if the reciprocating speed is increased, the mechanical loss is increased.
Although the third type electric toothbrush can considerably enhance cleaning performance by easily increasing the vibration frequency of the replacement brush, the invertor or the like is necessary. Therefore, there are problems that production cost rises and power consumption is also increased.
An object of the present invention is to provide a vibration generating device which is capable of effectively transmitting a high speed vibration and which can be produced at low cost, and an oral hygiene device using the same.